In Organic Cover Crops, More Seeds Means Fewer
Weeds

Farmers cultivating organic produce
often use winter cover crops to add soil organic matter, improve nutrient
cycling and suppress weeds. Now these producers can optimize cover crop use by
refining seeding strategies, thanks to work by an
Agricultural Research Service (ARS)
scientist.

In moderate climates, suppressing weeds in winter cover crops is important
because weeds that grow throughout the year produce seed that can increase
weeding costs in subsequent vegetable crops. ARS horticulturist
Eric
Brennan, at the
U.S.
Agricultural Research Station in Salinas, Calif., conducted studies
comparing winter cover crop planting protocols in organic systems along
Californias central coast.

Brennan looked at how seeding rates and planting patterns affected cover
crop performance. He planted rye using three seeding rates: 80 pounds per acre,
160 pounds per acre and 240 pounds per acre. The seeds were either planted in a
grid pattern that required driving a grain drill across fields twice, or in
traditional rows. All seeding was carried out in October.

Brennan found that planting rye at higher seeding rates consistently
improved early-to midseason rye biomass production and weed suppression. But he
saw no consistent crop improvement from grid planting.

Brennan also studied seeding rates and planting patterns using a cover crop
of legumes and oats. The seeds were planted at densities of 100, 200, and 300
pounds per acre and planted both in grids and traditional rows.

Results were similar to the rye cover crop results. As seeding rates
increased, weed biomass production decreased from around 267 pounds per acre to
less than 89 pounds per acre. In addition, planting patterns had no effect on
cover crop yield or weed suppression.

Brennans findings suggest that increased seeding rates could provide
organic producers with a cost-effective weed control strategy. However,
planting in a grid pattern would probably not consistently boost the benefits
of cover cropsand since it would require two passes through the field,
grid planting would likely double dust production, fuel use, planting time and
labor.